Core C FIELDWORK ? Summary: Gastric adenocarcinoma is the third leading cause of global cancer mortality and the leading cause of infection- associated cancer mortality, with marked geographic variability. In Latin America, geographic variability is manifest by the ?altitude enigma? where despite similarly high H. pylori infection rates, sharply contrasting high and low incidence rates are observed in the mountainous versus coastal regions, respectively, in the countries of the Pacific littoral zone. Core C is built upon long-standing, productive, and cost-effective research infrastructures in Colombia and Central America, each with sites in the high risk mountainous regions and lower risk coastal areas, and inclusive of populations that are racially and ethnically diverse. The Fieldwork Core C represents the epicenter to achieve the goals of this Program Project. Core C will oversee care of all the research activities carried out in Latin America, and provide the epidemiological data and human specimens to be used in all Projects and Cores. Our Core C specific aims are: (1) In Colombia, to execute all activities related to the oversight and follow-up of subjects in the Colombia chemoprevention cohort, with a focus on individuals who progress along the histopathology cascade, from chronic gastritis, to atrophy or intestinal metaplasia, and to dysplasia/adenocarcinoma. Studies central to Projects 1, 2, and 3 will focus on this group of progressors. (2) In Central America, to perform functions related to the recruitment of new subjects for the Central America cross-sectional H. pylori and human genetic ancestry study. The 3 sites include the high risk mountainous area (Copn, Honduras), and the low risk coastal sites located on the Caribbean (Tela, Honduras) and Pacific (Len, Nicaragua). This will provide an unparalleled research platform for the proposed genetic ancestry study, to further examine and explore the generalizability of our exciting findings regarding discordant co-evolution and gastric cancer risk. (3) To oversee the research infrastructures in Colombia and Central America, including data management, specimen collection and the biorepository. Core C will manage the Program Project epidemiology database to coordinate the interactions with the Projects and other Cores, provide overall quality control, and to track biospecimens. Core C will ensure that all data and specimens are de-identified in-country, in Colombia and Central America. In summary, the Colombia Fieldwork Core has been in place throughout the course of this Program Project, and we will now take this P01 in an exciting new direction by adding established sites in Central America to provide an unparalleled platform for our proposed clinical translational investigations into the mechanisms that govern gastric carcinogenesis.